This application claims the priority of Korean Patent Application No. 2003-64725, filed on Sep. 18, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, a channel time allocation method and apparatus according to characteristics of applications.
2. Description of the Related Art
A medium access control (MAC) protocol used in wireless communication systems adopts a carrier sense multiple access with collision avoidance (CSMA/CA) method and a time division multiple access (TDMA) method, in which a frequency band is shared between a plurality of users, according to its application. The CSMA/CA method includes generating a random number for each terminal, selecting a channel after a time equivalent to the random number, and using the channel if other terminals are not using the channel. Therefore, quality of service (QoS) does not depend on a terminal type or a transmission data type. However, the TDMA method allocates unique time slots with equal periods to each terminal on a given channel. Therefore, QoS does not depend on a terminal type or a transmission data type.
FIG. 1 illustrates a network topology according to the IEEE 802.15.3 standard.
A network includes a plurality of devices 101 through 104 and a piconet coordinator (PNC) 105 which relays and manages data and commands among the devices 101 through 104. A piconet is a network made up of a plurality of devices and a PNC. The devices may be home appliances, such as TVs and camcoders, and any of the devices can be the PNC 105. However, in general, an audio/video (AV) receiver or a computer is the PNC 105. The PNC 105 receives a channel time request command from each of the devices 101 through 104 and allocates a channel time to each of the devices 101 through 104. Each of the devices 101 through 104 directly transmits data to other devices at the allocated channel time. The PNC 105 also performs power save mode management and authentication management. Through the authentication management, the PNC 105 distributes a key for protecting a payload, and each of the devices 101 through 104 transmits and receives encrypted data using the allocated timeslot and the distributed key.
Each device used in the IEEE 802.15.3 standard smoothly enters and withdraws from a network, and in particular, it is preferable that a network entry time is less than one second. A MAC protocol of the IEEE 802.15.3 standard uses the TDMA method to guarantee QoS of streaming data.
FIG. 2 illustrates a configuration of a superframe to which a channel time is allocated.
The superframe includes a beacon 201, a contention access period (CAP) 202, two management channel time allocations (MCTAs) 203 and 204, and a plurality of channel time allocations (CTAs) 205 through 207. The beacon 201 is control information (an overhead) for transmitting data. The CAP 202 represents allocation of a channel time by contention, and a random access control based on the CSMA/CA is performed in the CAP 202. The MCTAs 203 and 204 are used for managing the plurality of CTAs 205 through 207. Payloads to be transmitted are allocated to the plurality of CTAs 205 through 207. Since one device can transmit several kinds of streams, a plurality of CTAs can exist. Synchronous data, such as an A/V stream, can be transmitted by obtaining a timeslot in a CTA, and asynchronous data can also be transmitted in a required band according to data size.
Since a TDMA MAC protocol is designed to be suitable for transmitting/receiving multimedia data, the TDMA MAC protocol cannot properly allocate existing asynchronous data. That is, when the existing asynchronous data should be transmitted, the asynchronous data can only be transmitted in a CAP field or a CTA field allocated during a contention free period (CFP).
On the other hand, since a CSMA/CA TDMA MAC protocol is designed to be suitable for transmitting/receiving asynchronous data, the CSMA/CA TDMA MAC protocol cannot properly allocate multimedia data. That is, when isochronous data should be transmitted, since the isochronous data is transmitted in a CAP field, QoS of jitter or delay is not guaranteed.
The IEEE 802.15.3 standard provides a method of handling a dependent piconet, such as a child piconet and a neighbor piconet. Accordingly, a private time that allocates a portion of a timeslot to each group and makes each group using the dependent piconet use the timeslot is used. However, in the dependent piconet, except for a PNC, no member of the dependent piconet can perform communication with any member of a parent piconet.